This invention relates to the preparation of select alkyl maleic anhydrides from alkenyl succinic anhydrides. Alkyl maleic anhydrides prepared in accordance with this invention are useful intermediates in the preparation of alpha-alkyl-beta-alkenyl succinic anhydrides which are known to be useful paper sizing agents and gasoline detergent additives.
A variety of processes for the preparation of alkenyl succinic anhydrides have been known and used for many years. For instance, U.S. Pat. No. 2,411,215, granted Nov. 16, 1946, and U.S. Pat. No. 3,819,660, granted June 25, 1974, describe the 1,2-addition reaction of monoolefins with maleic anhydride to prepare the corresponding alkenyl succinic anhydride. In general, the reaction proceeds according to the reaction scheme: ##STR1##
While alkenyl succinic anhydrides are useful products, there is a continuing need to develop a simple process for preparing alkyl maleic anhydrides. Toward this aim, it would be desirable to develop a means of isomerizing the alkenyl exocyclic double bond of alkenyl succinic anhydrides back into the anhydride ring to form alkyl maleic anhydrides.
The use of various acid catalysts to isomerize aliphatic alkenes is described in the prior art. For instance, Noller (Ed.), "Chemistry of Organic Compounds 3rd", W. B. Saunders (1966) describes the acid-catalyzed interconversion of 1-butene and cis- and trans-2-butene. Additionally, Noller discloses the thermally induced rearrangement of itaconic anhydride to citraconic anhydride.